In high fidelity loudspeaker design, the aim is to reproduce sound without added colonization. The loudspeaker is designed so that the diaphragms of the drivers are displaced by electromagnetic forces to create vibrations, which emulate the original sound as accurately as possible. The design principle is that only the sound producing diaphragms of the drivers vibrate while the cabinets, which enclose the drivers, are designed to absorb as much conducted vibration as possible so that only sound waves made intentionally by the driver diaphragms are communicated to the listener. The sound waves are reproduced by an oscillating diaphragm, which is driven by voice coil deviated with electromagnetic forces and which is suspended from the driver chassis by a surrounding elastic rim that allows the diaphragm to move back and forth. The driver chassis is typically connected to the loudspeaker cabinet with a flange joint, wherein a flange of the driver chassis is bolted or otherwise fixed to the outer surface of the cabinet having an opening for accommodating the rear portion of the driver. Between the surface of the cabinet and the inner surface of the driver chassis flange is typically adapted a ring for sealing the engagement.
While the object is to reproduce sound waves by vibrating only the diaphragm of the driver, some vibration is however known to conduct to the cabinet thus impairing the output of the loudspeaker. The same force that is moving the sound producing diaphragm also applies force to the rest of the driver e.g. the magnet and chassis. Because the mass of the magnet, the driver chassis and the rest of the driver is large compared to the mass of the diaphragm, the actual fluctuating movement—or vibration—of the rest of the driver is very small. Nevertheless, this incurred secondary force causes unintended vibration, which is ultimately conducted through the driver coupling onto to emanate around the mechanical structures of the loudspeaker. Problems are emphasized by the fact that mechanical structures have at least one resonance frequency, in which small vibrations are amplified by the structure itself. In fact, mechanical resonances can differ in different parts of the structure, wherein the resonance frequencies can be local. For example, the side wall of the loudspeaker can resonate on a different frequency than that of the rear wall. This is why mechanical resonance add unintentional color to the sound output in the resonance frequency. Depending on the mechanical source of the resonance, the frequency may be different in directions of sound output. Due to this problem the cabinet of the loudspeaker is designed such that the vibration traveling around the walls is gradually absorbed in the losses of the enclosure.
The vibration impairing the loudspeaker output is therefore the result of unintended excitation of the enclosure in which the driver is mounted. Excitation of the loudspeaker cabinet is, to a large extent, a well known problem. So far, improvements have been made to driver mountings to decouple the driver mechanically from the enclosure. On the other hand additional improvements have been made to the loudspeaker cabinets, which are designed to absorb as much vibrations as possible. Publication EP 0917396 discloses a method and arrangement for attenuating mechanical resonance in a loudspeaker, wherein a reactive additional mass is used for dampening enclosure excitation. The arrangement can, however, only be tuned to a specific frequency, which is efficient in said frequency, but cannot provide a universal solution to a variety of resonances in different frequencies. Conventional prior solutions utilize driver mountings featuring decoupling from the cabinet with a seal, such as a rubber mount, between the driver chassis flange and the loudspeaker cabinet. The elastic seal secures the driver chassis tightly to the cabinet while providing partial mechanical decoupling in terms of preventing the vibrations from conducting onto the cabinet.
However, known driver mountings have so far not been able to eliminate unintentional excitation of the loudspeaker cabinet to the extent, where output of the loudspeaker is not compromised by the above described recoil effect. Enclosure structures having either very thick walls or laminate walls comprising dampening material in between frame walls have been proposed, but in practice such structures complicated and expensive. Solutions featuring reactive dampeners and other sprung mass constructions provided between the drive unit and the enclosure, on the other hand, only attenuate vibrations in a single frequency.